Method of sintering



1940? J. E. GREENAWALT 2,191,911

METHOD OF SINTERING Filed March 2, 1938 QTTOPA/EK Patented Feb. 27, 1940 UNITED STATES PATENT I am My invention has relation to improvements in methods of sintering and it consists in the novel features more fully set forth in the specification and pointed out in the claims.

Essentially the invention is in the discovery that a sintering temperature, once properly initiated, can be maintained,,,and propagated throughout 'the'entire charge with less fuel than that required to initially start the sintering action. The discovery is effectively carried out by the manner in which the charge of material to ignited and suction applied to the charge to propagate the sintering action downwardly through the charge.

It is well known in the metallurgical art that much difficulty is often encountered in successfully sintering ores for the subsequent treatment a in the blast furnace, for, in addition to the production of a structurely strong sinter, it is desirable that the sulphur content of the ore be almost completely .eliminated and that the formation of iron'silicates in the resulting sinter be ll prevented almost completely, since the reduction of these silicates in the blast furnace is accomplished with great difilculty.

Of course, in addition to these desiderata, it is also essential, where large tonnages of ore are 6 treated, that the sintering operation be performed quickly and thoroughly as a matter of economy of operation.

Various expedients have heretofore been tried to effect these results with varying degrees of success, including the method disclosed in my Patent No. 1,799,163, wherein the charge is arranged in a sintering pan in successive layers of different sized particles. However, as far as I am-aware, no one has heretofore recognized the far-reaching results that are obtained in constituting a charge for sintering in which a relatively thin layer of the material having a high fuel content is superposed on' the main body of the charge carrying a low fuel. content.

Among the objects accomplished by thus constituting a sintering charge are:

1. The reduction of the amount of fuel necessary for producing a strong sinter.

2. The more complete-elimination of sulphur, 5. especially from ferrous ores.

3. The prevention of the formation of iron silicates.

4. The more rapid and complete sinteringof a given-charge. 10

The invention, together with the advantages thereof, will be better understood from a detailed description in connection with the accompanying drawing, in which the figure represents a vertical longitudinal section through a sintering pan of conventional type, over which is superposed an igniting hood for effecting initial ignition of the charge disposed within the pan.

Referring to the drawing, I represents a sintering pan provided with the usual grate 2 for supporting the sintering charge C, and having hollow trunnions 3, 3 through which suction is applied to the charge and upon which the pan is rotatable for dumping. Initial ignition ofthe charge C is effected bya Greenawalt-type igniting hood 4 equipped with burners 5, 5 for filling the hood with flame when ignition of the charge is to be effected. c

The igniting hood and burners are of the same general construction shown in my pending application, Serial No. 128,362, filed March 1, 1937, and the method of igniting the charge is substantially the same as that forming the subject matter of said application.

The charge 0 of material to be sintered is disposed in the sintering pan in two superposed layers of different composition, the lower layer m of which constitutes the main body of the charge containing a minimum amount of fuel for sustaining the sintering action. Of course, the amount of fuel depends largely upon the composition of the material and the amount of sulphur contained therein. In the case of red ores of iron, such as the hematites and limonites, the layer m would contain about 3 /2% of carbon in the form of coal or coke.

A thin layer m of the same material as th layer m except that it carries a'higher fuel content (.approximately 7% of carbon) is superposed directly on the layer m, and after being ignited by the flame within the hood 4 is brought to a sintering temperature, which temperature is rapidly communicated tothe charge beneath and. thereby initiates a sintering temperature in the top of the charge m and this sintering tempera- ,r

ture is transmitted and propagated to the portion of the charge directly beneath it, and so on until the entire charge has been sintered. The essence of this invention resides in the discovery that a sintering temperature once properly initiated by means of a thin top layer containing the necessary fuel can be maintained and propagated through a charge containing much less fuel than that necessary to start or initiate that sintering temperature.

The primary function, therefore, of the thin layer m is to initiate a sintering temperature in a chargecontaining insufiicient fuel to accomplish this result and also contribute to the maintenance and the propagation of this temperature throughout the charge. The fuel content of the layer m is just suflicient to maintain combustion therein and the propagation of the sintering action from the top to the bottom thereof and does not utilize as much oxygen as a higher fuel content. Therefore, there is plenty of free oxygen passing through the layer m to combine with the sulphur therein and effect an almost complete elimination thereof. Furthermore, the reduction of the fuel content in the layer m below what is ordinarily used in sintering operations greatly speeds up the sintering action, so that the intense heat for sintering does not remain sufiiciently long in any locality in the charge to causethe formation of iron silicates therein.

The formation of iron silicates is avoidedv due to the fact that the temperature obtained is just suflicient to do the sintering, but is below the temperature necessary for the formation of iron silicates, and also because the time required for the sintering zone to pass a certain point was too short for the oxide of iron to be fused with the silica. Iron silicates in sinter are very objectionable in the blast furnace, as they are difficult to reduce and tend to reach the lower zone of the furnace in unreduced form.

The main body of the charge m is from nine to ten times the thickness of the layer 122. A layer m of less than this-thickness may be effectively sintered, but would not be considered economical practice as the layer should be as thick as is consistent with satisfactory results. However, the thickness of the layer m is limited because of the increase in suction required to draw air in sufiicient volume to support combustion downwardly through the charge. Obviously, a thicker layer would require the suction be increased sufficiently to increase the velocity of the air currents passing through the charge on account of the] greater amount of oxygen necessary to support the combustion therein. I have discovered that all the requisitesfor practically complete sintering are met by limiting the thickness of the superposed layers m and m and fixing the fuel content of said layers as above set forth.

than .10% in order to be available forthe blast furnace.

In sintering the ore by the methods heretofore utilized, the sulphur elimination was unsatisfactory if suflicient fuel was used to produce a goodsinter, and upon reducing the fuel content, better sulphur elimination was obtained but at the cost of complete sintering. The upper part of the charge particularly was only partially sintered.

However, upon arranging the charge, which was 14" thick, as herein described with a 1 layer at the top containing about 5% of fuel and only 2 of fuel in the balance of the charge, practically the entire charge was completely sintered and the sulphur content was reduced to approximately .05%. The speed with which the sintering zone passed through the charge was alsogreatly increased and there was practically no fusion of the sulphur compound and no forably is just suificientto maintair. sintering action throughout the layer, which in ures low temperature sintering essential -in --;he avoidance of fusing the sulphur content of the means formation of iron silicates.

Having described my invention, I claim:

1. The herein described method of sintering ores containing silica, which comprises the arranging of a charge of the finely divided material to form a homogeneous mass with a fuel content below that necessary to effect direct ignition thereof, superposing on the mass a thin layer of material having a greater fuel content than that contained in the mass, igniting the surface of the superposed layer, causing a supporter of combustion to traverse the mass downwardly to effect complete sintering of the mass at a temperature below that necessary for the formation of iron silicates.

2. The herein described method .of sintering ores containing silica and sulphur, which comprises the arranging of a charge-of the finely A divided material to form a homogeneous mass with a sulphur content below that necessary to the surface of the charge, causing oxygen to traverse the mass downwardly in sufficient quantity to eliminate the sulphur content of the material and effect sintering at a temperature below that required for the formation of iron silicates.

JOHN E. GREENAWALT. 

